Benzoxazine compounds can be synthesized by reacting a phenol with an amine and an aldehyde in the presence or absence of a solvent. The benzoxazine product is then isolated from the reaction solution by evaporation or precipitating the product from solution via a poor solvent.
In U.S. Pat. Publ. No. 2010/0210810, a process is disclosed for preparing high molecular weight benzoxazines which includes reacting a bifunctional phenol with a diamine and an aldehyde in a mixed solvent system containing an aromatic nonpolar solvent and an alcohol. Condensation water is then subsequently evaporated and the benzoxazine may be recovered from the reaction mixture by precipitation or spray-drying.
U.S. Pat. Publ. No. 2009/0270615 discloses a process whereby benzoxazines are produced from a phenol, primary amine and an aldehyde in the presence of an alkyl ester. The alkyl ester is then subsequently removed at moderately low temperatures.
In a process disclosed in U.S. Pat. No. 7,041,772, a phenol is reacted with a primary amine and aldehyde in an organic solvent selected from an alcohol, ketone, ethylene glycol and aromatic type solvent. Condensation water and organic solvent are then subsequently removed from the system under heat and reduced pressure to produce a benzoxazine.
U.S. Pat. Publ. No. 2009/0054614 teaches a process wherein a specific phenol is reacted with a specific aromatic diamine and an aldehyde optionally in the presence of an aromatic, halogenic or ether solvent to produce a dihydrobenzoxazine. Methanol is subsequently added to precipitate the dihydrobenzoxazine product from solution, and the precipitate is then dried to form the dihydrobenzoxazine product.
U.S. Pat. Publ. No. 2009/0187003 also discloses a process for making a dihydrobenzoxazine from an aromatic phenol, an aliphatic diamine and an aldehyde in the presence of an aromatic, halogenic or ether solvent. The benzoxazine is precipitated from solution using a poor solvent and then dried.
Finally, U.S. Pat. No. 5,543,516 teaches a solventless method for preparing benzoxazines from a phenol, a primary amine and aldehyde.
Known processes for producing benzoxazines are, however, not without their difficulties. For example, it usually takes a relatively longer time than desired to carry out the reaction and separate the benzoxazine from the solvent and condensation water. In addition, some of the solvents used in the synthesis are toxic while others are only removable at elevated temperature conditions causing premature degradation and/or polymerization of some benzoxazine compounds. Furthermore, when the condensation water and solvent are removed under significantly reduced pressure, the temperature of the reaction solution abruptly drops causing the viscosity of the solution to increase making further processing and use extremely difficult.
Notwithstanding the state of the technology, it would be desirable to provide alternative methods for producing benzoxazines whereby the benzoxazines are easily obtained as a powder solid with low residual solvent content and with substantially reduced or no gelation occurring during their production.